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I have done some searching around and can't seem to find an exact answer to my question. It seems like it should work but it doesn't. Here's my code:

typedef struct stack_strut 
 Item* top;
 int size;
stack;

void initialize(stack* s) 
 s = (stack*)malloc(sizeof(stack));
 s->size = 0;


int main() 
 stack s;
 initialize(&s);
 return 0;

That's a condensed version obviously. I was under the impression that I'd be able to modify the contents of the struct since I'm passing a pointer to it, so a change a make inside the function should stick around after it returns. If I use a print statement inside the initialize function to check the size, it successfully prints 0. However, If I use another print statement in main immediately after initialize returns, the size of s is now a very large number. Is it because I didn't initialize s outside the function? I have to keep it in this format because the main function supplied by my professor starts off in the same way:

stack s;
initialize(&s);

The issue is when you write s = (struct*)malloc(sizeof(strucy)); it overwrites the pointer to s and you do not initialize the "good" object. You created an other one and initialized it (memory is leaked). You can check by printing the value of

The malloc is not needed the s stack is already allocated in main

#include <iostream>

struct Item 
 int nodeId;
;

struct stack 
 Item* top;
 int size;
;

void initialize(stack *s)

 std::cout << "initialize 1. stack at " << s << std::endl;
 s = (stack*)malloc (sizeof(stack));
 std::cout << "initialize 2. stack at " << s << std::endl;
 s->size = 0; 



int main() 
 stack s;
 std::cout << "main 1. stack at " << &s << std::endl; 
 initialize(&s);
 std::cout << "main 2. stack at " << &s << std::endl; 
 return 0;

will output (see initialize 2.)

main 1. stack at 0x7ffca7c72520
initialize 1. stack at 0x7ffca7c72520
initialize 2. stack at 0x5566830b0280
main 2. stack at 0x7ffca7c72520